(a) Field of the Invention
The present invention relates generally to a microflow controller, and more particularly to an integrated thermister type flow control module.
The present invention is applicable for use on all kinds of microflow control apparatus. For instance, the present invention is particularly adapted to couple with microvalves and to be synchronously manufactured therewith on the same substrate. The present invention is also particularly adapted for use in micro control of gases.
(b) Description of the Prior art
A study of the microflow elements and systems made using existing micromachining techniques shows that they are characterized in their capability to precisely sense and control micro amounts of fluid. In general, for gases, the amount of flow controlled is below 1 l/min. For liquids, it is about .mu.l/min. Aside from being capable of precisely sensing and controlling micro amounts of fluid, the microflow elements and their systems have the advantages of power economy, quick response time, and compactness. Furthermore, due to the characteristics of micro manufacturing techniques, different sensors, actuators, and control circuits can be integrated on the same chip. Therefore, they can provide systematic, multi-functional, and even intelligent microflow system modules within very small units. The microflow elements can also be assembled in arrays to achieve precision control of larger flows. At present, the application of microflow mechanical devices has possibly replaced traditional precision flow control elements in part or made it possible to develop compact fluid sensors. In the future, when the development of micro manufacturing techniques and sensors has become more mature, the applications of microflow will be more comprehensive and become multi-functional and intelligent, which will then have a huge impact on industries.
In U.S. Ser. No. 08/667,906 filed on Aug. 27, 1996 by the applicant of the present invention, various prior art techniques concerning microvalves have been generally discussed. These prior art techniques include U.S. Pat. Nos. 5,142,781, 5,180,623, 5,058,856, 5,271,597, 5,259,737, and 5,429,713, as well as the papers entitled "Microflow Devices and Systems" (pages 157-171, Micromech. Microeng. published by IOP, U.K. in April 1994) and "Integrated Microflow Control Systems (pages 161-167, Sensors and Actuators, The Netherlands, 1990). T. Lisec et al. have also discussed thermal buckling control of microvalves on pages 13-17 of IEEE, 1994.
The present invention is the applicant's continued study on micromachining to further exploit the advantages thereof.
In today's precision analysis instruments and semiconductor manufacturing equipment, mass flow controllers (MFC) are often used to provide precision control of gas flow. The components of MFC include independently made precision control valves, flow sensors and system controllers. Electromagnetic or piezo-electric valves are generally used as precision control valves, whereas capillary heating type flow sensors are used as sensors. Since all components are made by ultra-precision machining techniques and finished by employing mechanical sealing techniques, the parts of the entire system are many and complicated. Assembly is difficult and manufacturing cost is therefore high.